linux-kernel - Re: [PATCH v5 00/13] riscv: improve boot time isa extensions handling

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Date:   Sun, 12 Feb 2023 18:20:03 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Jisheng Zhang <jszhang@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Andrew Jones <ajones@...tanamicro.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org
Subject: Re: [PATCH v5 00/13] riscv: improve boot time isa extensions handling

On Sun, Feb 12, 2023 at 10:14:13AM -0800, Guenter Roeck wrote:
> On 2/12/23 10:06, Conor Dooley wrote:
> > On Sun, Feb 12, 2023 at 05:06:09PM +0000, Conor Dooley wrote:
> > > On Sun, Feb 12, 2023 at 04:33:58PM +0000, Conor Dooley wrote:
> > > > On Sun, Feb 12, 2023 at 03:59:59PM +0000, Conor Dooley wrote:
> > > 
> > > So as not to lead anyone up the garden path, let me correct myself:
> > > 
> > > > Hmm, so this appears to be us attempting to patch in alternatives where
> > > > none actually exists - seemingly F & D.
> > > 
> > > And of course that's not true, riscv_has_extension_likely() now uses
> > > alternatives as of:
> > > bdda5d554e43 ("riscv: introduce riscv_has_extension_[un]likely()")
> > > 
> > >  From a quick look, it just happens that the only users are F & D.
> > > 
> > 
> > Samuel pointed out that this is a lockdep splat on irc.
> > There's a patch on the list that removes the lockdep annotation
> > entirely:
> > https://patchwork.kernel.org/project/linux-riscv/patch/20230202114116.3695793-1-changbin.du@huawei.com/
> > 
> > So ye, no surprises that it was config based!
> > 
> > Palmer posted a "better" fix for that lockdep warning a while ago:
> > https://lore.kernel.org/all/20220322022331.32136-1-palmer@rivosinc.com/
> > 
> > So we'd have to duplicate/reuse that for cpufeature/errata patching.
> > 
> > 
> 
> This does not (only) happen in stop_machine().

Yah, sorry I meant that it's the same lockdep splat as is being
addressed there.
The first patch deletes the lockdep stuff entirely, so removes the
splat. I was thinking that we'd need to take Palmer's (IMO better)
patch and do the same thing for patching alternatives, but I figure we
can just take the text_mutex itself for alternatives & not have to
dance around the lock.

I'll go do that I suppose!

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